The present invention relates generally to detecting flaws in optical fibers and, more particularly, to a system for detecting flaws in an optical fiber wherein a laser beam is directed upon the optical fiber in a direction substantially orthogonal to the fiber axis and the portion of the laser beam which is scattered outside of a radial plane substantially perpendicular to the longitudinal axis of the optical fiber by beam flaws is monitored to detect those flaws. An apparatus for calibrating the detector is provided which comprises a movable cartridge containing an optical fiber sample having a known flaw. The cartridge is translated in the laser beam and the detector is adjusted to respond to the scattering of the laser beam by the known flaw.
Due to their excellent transmission characteristics, optical fibers are being increasingly used as signal carriers not only in communication systems but also in a wide variety of other applications including weapon systems and medical diagnostic instruments. Generally, optical fibers consist of a fiber core surrounded by a fiber cladding which has a lower index of refraction than the fiber core. Within the layers of an optical fiber, nonuniformities may occur as a result of the faulty fabrication or improper handling of the fiber. The nonuniformities may include, for example, bubbles, lumps, neckdowns, coating defects, surface contamination, core contamination and the like.
Such nonuniformities may increase the signal losses in the fiber or, in the extreme, completely terminate signal transmission. It is apparent that these deleterious effects of defects or flaws in the optical fiber may result in malfunction of a device in which the fiber is employed. Consequently, optical fibers must be carefully examined to detect any such defects or flaws.
Fiber optic flaw detection systems which direct a laser beam toward an optical fiber and monitor the refraction and diffraction of the laser beam to detect flaws are known in the art. For example, U.S. Pat. No. 4,924,087 issued to Bailey et al. discloses a fiber optic defect detection system wherein the optical fiber to be examined is extended axially through a dish-like structure and illuminated by one or more laser beams directed substantially orthogonal to the fiber axis. For a flaw free optical fiber, the laser beam is scattered by the optical fiber onto a light-absorbing band on an inner surface of the dish as in-plane scattered rays. For an optical fiber having a flaw, a portion of the laser beam is scattered outside the band as out-of-plane scattered rays. Out-of-plane rays which deviate a sufficient amount from the band illuminate an aperture located above the band and are detected as flaws.
Unfortunately, the Bailey et al. flaw detector does not respond to out-of-plane light rays which are scattered below the light-absorbing band such that this detector is at best not as sensitive as possible when detecting flaws which only cause such scattering or predominately scatter rays in that direction. Accordingly, a need still exists in the art for an improved approach to flaw detection in optical fibers which is fast and reliable, accurately detects flaws, is easy to operate and is easily and accurately calibrated.